The present invention relates to novel photoresist compositions and methods of making and using such compositions. More particularly, the present invention provides photolithographic methods for making photoresists by applying a mixture of a polyimide having at least one pendant aromatic radical and a bis-maleimide to a substrate and allowing it to dry, and thereafter exposing the thus treated substrate while it is masked to a source of light so as to effect crosslinking of the polyimide and bis-maleimide.
Prior to the present invention polyimides and polysiloxane imides were obtained by effecting reaction between a carboxylic acid dianhydride and a diamino compound and/or diaminopolysiloxane to obtain an initial reaction product having the formula, for example, ##STR1## Upon heating at a temperature of about 150.degree. C. to 350.degree. C. the polymeric amido compound cyclized to yield an imidized composition of recurring units of the formula, for example, ##STR2## This method is described more fully in U.S. Pat. Nos. 3,325,450 and 3,553,282, among other patents and literature references.
Photoresist materials which are based on a photoreactive precursor are described by Rubner et al. in "Production of Highly-Heat Resistant Film Patterns from Photoreactive Polymeric Precursors, Part I, General Principles (January: 1976)" and "Production of Highly-Heat Resistant Film Patterns from Photoreactive Polymeric Precursors, Part 2, Polyimide Film Patterns (May 1976)". A photoreactive polyamide is made by initially effecting reaction between an aromatic dianhydride, for example, pyromellitic dianhydride, and allyl alcohol. The resulting aromatic dicarboxylic acid diester is then converted to the corresponding aromatic diacid chloride by reaction with thionyl chloride. The diacid chloride is further reacted with an aromatic diamine to produce a photoreactive aromatic polyamide ester. The aforementioned photoreactive polyimide precursor is then applied to a substrate, for example by spin coating, and exposed to light with the aid of a mask, followed by developing the treated surface with an organic solvent to produce a photoresist. The aromatic patterned polyamide ester is then heated to convert it to a patterned polyimide.
Although valuable results have been achieved with the aforementioned photoreactive aromatic polyamide ester, those skilled in the art recognize that the use of a chlorinating agent such as thionyl chloride to convert the aromatic dicarboxylic acid to the corresponding acid chloride prior to the polymerization reaction with aromatic diamine can result in the introduction of residual chloride contamination. Such chloride contamination can interfere with the utility of the resulting aromatic polyimide as a dielectric.
It is also desirable to avoid the heating step required in the foregoing process which is necessary to convert the patterned polyamide ester to a patterned polyimide.
It is, therefore, desirable to provide a photosensitive composition useful as a photoresist and convertible to a patterned insulating layer which does not require heating to effect imidization.